1. The Field of the Invention
The present invention relates to the use of low frequency energy (in the acoustic range) to selectively affect the permeability in a reservoir to control fluid flow and, in particular, to a technique involving the use of synchronized vibratory sources spaced in a patterned array with respect to the reservoir to impart low frequency energy which can be focused selectively on localized zones within the reservoir.
2. The Prior Art
It is well known to use acoustic wave energy for the purpose of making seismic surveys, see U.S. Pat. No. 4,008,459 for example. It is also well known to impress a coding format on these acoustic wave signals to obviate problems with interference and/or false returns, see U.S. Pat. No. 4,969,129 for example. It is further well known to place acoustic wave generating sources down well bores and to conduct seismic surveying subsurface between wells, see U.S. Pat. No. 5,042,611 for example. However, no one to date has proposed to apply acoustic wave energy to a formation in such a manner as to improve the production therefrom.
There are a number of publications which suggest that the application of acoustic energy to a reservoir can possibly have an effect on the volume of fluids produced therefrom. This phenomena is not well understood and is not commonly used in the United States at this time. Although work was done in the area in the United States over twenty years ago, it was not subsequently actively pursued. The technique has been used to some extent in the former Soviet Union. There has been a recent revival of interest in this concept in the United States by several major oil companies.